Numerical control servo-system



J. w. FORRESTER ETAL 3,069,608

NUMERICAL CONTROL SERVO-SYSTEM Dec. 18, 1962 15 Sheets-Sheet 1 Filed Aug. 14, 1952 OKNOQONO G mlwhmaum alien m x 6 wca x $6. PINE-DOW mzuhmawt JOE mmvroxs JAY w. FORRESTER WILLIAM M. PEASE JAMES O. MCDONOUGH ALFRED K. SUSSKIND BY /H/ Dec. 18, 1962 J. w. FORRESTER EIAL 3,069,603

NUMERICAL CONTROL SERVO-SYSTEM 15 Sheets-Sheet 3 Filed Aug. 14, 1952 llll I w iwmuziuu zo l I I INVENTORS JAY W. FORRESTER WILLIAM M. PEASE JAMES O. MCDONOUGH ALFRED K. SUSSKIND BY Ym AHv Dec. 18, 1962 J. w. FORRESTER ETAL 3,059,608

NUMERICAL CONTROL SERVO-SYSTEM l5 Sheets-Sheet 4 Filed Aug. 14, 1952 INVENTORS JAY W. FORRESTER WILLIAM M. PEASE JAMES O. MCDONOUGH ALFRED 1962 J. w. FORRESTER ETAL 3,

NUMERICAL CONTROL SERVO-SYSTEM 15 Sheets-Sheet 5 Filed Aug. 14, 1952 INVENTORS JAY W. FORRESTER WILLIAM M. PEASE JAMES 0. MC DONOUGH ALFRED K. SUSSKIND Dec. 18, 1962 J. w. FORRESTER ETAL 3,

NUMERICAL CONTROL SERVO-SYSTEM 15 Sheets-Sheet 6 Filed Aug. 14, 1952 INVENTORS FORR ESTER WlLLIAM M. PEASE JAY W.

JAMES O. MCDONOUGH ALFRED K. SUSSKIND Dec. 18, 1962 J. W. FORRESTER ETAL NUMERICAL CONTROL SERVO-SYSTEM Filed Aug. 14. 1952 INPUT TO FIRST FLIP-FLOP l5 Sheets-Sheet 8 Fig. 8

TIME

NONCARRY OUTPUT OF FIRfiT FLIP-FLOP CARRY OUTPUT OF FIRST FLIPFLOP= INPUT TO SECOND FLIP-FLOP NONOARRY OUTPUT OF SECOND FLIP- FLOP CARRY OUTPUT OF SECOND FLIP-FLOP, TO START-STOP CIRCUIT TOTAL NONOARRY OUTPUT OF FREQ.

DIVIDER I SYNCHRO' NIZING PUL5E$ IOO NONCARRY PULSES Fig. I4 448 GCO FROM FIRST STAGE L OF FREQ. DIVIDER I NoNcARRY PuLsEs FROM 2' STAGE. OF FREQ. DIVIDER I (NONCARRY PULSES FROM ALL STAGES OF FREQ.D|\I.1I AND CARRY PULSES FROM LAST 5T\AGE OF FREQ. DIVIDER 11.,

GCI. GCZ

INVENTORS JAY W. FORRESTER WILLIAM M. PEASE JAMES O. McDONOUGl-I ALFRED K. SUSSKIND mam? - Dec. 18, 1962 J. w. FORRESTER ETAL 3,069,608

NUMERICAL CONTROL SERVO-SYSTEM l5 Sheets-Sheet 10 Filed Aug. 14, 1952 EOFOI nuwam PIS-M200 (Fa MESH! wmm Dec. 18, 1962 J. w. FORRESTER ET AL 3,069,603

NUMERICAL CONTROL SERVO-SYSTEM 15 Sheets-Sheet 11' Filed Aug. 14, 1952 i i Lyn mvm 2 muoouuo INVENTORS FORRESTER JAY W.

WILLIAM M. PEASE JAMES O. MCDQNOUGH ALFRED K. SUSSKIND BYMY 4 Dec. 18, 1962 J. w. FORRESTER ET AL 3,069,608

NUMERICAL CONTROL SERVO-SYSTEM Filed Aug. 14, 1952 15 Sheets-Sheet 12 Fig. l3

OUTPUT E VO :TAG E OUTGOING PULSE LEADS TO POSITION CODE CONVERTER Fig. l2

INVENTORS JAY W. FORRESTER WILLIAM M. PEASE JAMES O. MCDONOUGH ALFRED K. SUSSKIND Dec. 18, 1962 J. w. FORRESTER ETAL 3,069,608

NUMERICAL CONTROL SERVO-SYSTEM Filed Aug. 14, 1952 15 Sheets-Sheet 15 Fig. I? 02 I l x boo 000 00 o 000 0000 o o o o 00 E- v -c ooo 0 00000 000 000 zo o oo o oo oo o o 000 o 00 000 OOOOOOOOQQOOOGOGOGO00000DOQQOOQOOOOOOQGOOGOOG 00 08 000 80 0 8 0 0 0 0 0s 00 v 200 -o o o oo o0 'o 00 000 00 0' 205 00 0000001 looooooool INVENTORS JAY W. FORRESTER WILLIAM M. PEASE JAMES O. MCDONOUGH ALFRED K. SUSSKIND United States Patent 3,059,608 NUMERIQAL CONTROL SERVO-SYSTEM Jay W. Forrester, William M. Pease, and James 0. Mc-

Donough, Concord, and Alfred K. Susskind, Cambridge, l'viass., assignors, by mesne assignments, to John T. Parsons, Danville, Ill.

Filed Aug. 14, 1952, Ser. No. 304,24 69 Claims. (Cl. 318-162) This invention relates to control systems and particularly to a novel method of and apparatus for controlling the operation of industrial appliances and processes such as machine tools and the like.

The general purpose of this invention is to provide an improved control system which is especially desirable for machining mathematically definable surfaces without resorting to the expensive practice of first constructing models or templates having better than the required accuracy of the finished work. In such use, the present invention enables the machining or shaping of work which is not limited to lines parallel to the machine-feed directions but permits any cutting or shaping operation along any line skewed or inclined with respect to the machinefeed directions. No models or templates are required to perform the coordinated motions in the machine-feed directions and instead, information for controlling the machine may be stored in coded form on simple, convenient mediums such as punched paper tape, punched cards, magnetic tape, photographic film, et cetera. Electrical means is employed for interpreting the coded information and for transmitting the information in electrical form to the one or more moving operating parts of the controlled unit or machine. The result is that the control system or director may be located remote from the machine and be used not only to control one but several similar machines.

Although the invention is applicable to the control of the movement and positioning of one or more moving parts of various types of apparatus, it is especially applicable to the shaping or sculpturing of objects and particularly the machining of templates, forging dies, stretch form dies, airfoil sections, et cetera. Conventional die making and similar shaping processes are usually 1aborious, time consuming, painstaking operations requiring the production of checking templates, and final hand finishing to produce an accurate die. The present inven tion eliminates the production of template and in most instances reduces the necessity for hand finishing of the die or other object worked on at the same time permitting smaller tolerances than those usually required by present day standards. The elimination of the tedious hand operations as well as the production of templates, considerably shorten the diemaking time.

An important object of the invention is to provide a control system for a machine, such as a milling machine, which incorporates a pulsed sensing electrical circuit and provides binary-dividedpulse rates properly phased to interpret the commands on medium containing the stored control information. The control system is designed to employ digital technique to maximum advantage and requires only a single enumerating specification. An important feature of the invention is the integration of the rate and position commands into one system enabling the use of a single medium upon which the stored information is carried.

Another important object of the invention is to provide a control system which insures synchronism between the various motions of the machine and which converts the information provided in digital form into the analog form finally embodied in the machined workpiece. An important feature of the invention is the use of a common time parameter in the digital domain for coordinating all 3,069,608 Patented Dec. 18, 1962 motions included in the control system. Another important feature of the invention is the provision for selecting a choice of ratios available in the digital domain which are readily changeable to various speeds.

Another important object of the invention is the elimination of the necessity of separate orders or commands for the rate of advance of one or more machine operated parts and for governing the position thereof. The invention provides a single set of binary-divided pulse rates which generate machine time and machine space, both having the same dimensions expressed in pulses thereby eliminating the necessity of providing separate orders or commands for the rate and the position of the operating parts controlled thereby.

Another important object of the invention is to provide a novel method of and means for synchronizing command pulses governing the action of one or more controlled parts or servo-mechanisms with response pulses for substantially simultaneously synchronizing the input commands with the output responses in order that the system may behave as nearly like a continuously operated system as possible.

Another important object of the invention is to provide improved means in the system for storing and comparing the input commands and output responses in incremental form and for simultaneously subtracting one from the other to obtain a differential or error signal for controlling the movement of one or more servomotors. In carrying out this object there is provided a reversible counter which approximates a continuous differential for an error detecting or summing device and which enables the output to be compared with the input substantially simultaneously and while storing only the maximum error and not the entire command number.

Another important object of the invention is to provide a master or clock oscillator which generates a series of pulses spaced in time, each pulse of which may represent an instruction to an operating part of the machine to move one unit of distance. An important feature of the invention relates to the provision of a frequency divider associated with the clock oscillator which generates a pattern of potential command pulses for governing the operation of the servo-mechanisms. Another important feature of the invention is the novel association of the frequency divider with an information storage medium responsive to coded information on tape or otherwise which impresses the stored information into the potential command pulses provided by the frequency divider.

Another important object of the invention is to provide a counting-error detector which functions to subtract the output from the input pulses and is reversible to approximate a continuous error-detecting or summing device. The counting error detector has a register capacity which by virtue of its construction and function need only be large enough to store the maximum differential or error between the input and output pulses, which differential or error is utilized to control the operation of one or more servomotors. In consequence, the digital conversion of the output and the input is in pulses and in a differential or error channel where the signals are relatively small. The digital conversion to the analog commands is inside the loop of one or more servo-mechanisms employed in the machine and as a result the analog uncertainty is limited to an arbitrarily small percentage of the total signal handled.

Another important object of the invention is to provide a code converter in the form of a sensing system operating on pulses and which permits the use of synchronizing sensing pulses for accuracy and checking.

Another important object of the invention is to provide a dual storage system which allows the machine to operate continuously from discontinuously obtained data furnished by coded media such as punched tape. The dual storage system comprises two storage registers which are alternately operable to impress the information stored therein into the potential command pulses for operating the servo-mechanisms.

Another important object of the invention is to provide means for checking the operation of the machine parts and particularly the use of a counter as an error detector which provides one pulse in a series of pulses for each cycle of information. This pulse is preferably the last of the series of pulses provided for each cycle of information and is used as a check on the system to avoid any unannounced loss of synchronism either in the control system or in the functioning of the servo-mechanisms.

Another important object of the invention is to provide a novel method and means for detecting or sensing the direction in which an operating part or tool of the machine has moved. This is accomplished by the provision of a novel position coder which transmits outgoing pulses in separate circuits, the sequence of such pulses being alterable depending upon the position of the operating part for controlling the direction of the future movement of the part. These signals, in the form of pulses, are carried Within the loop of the servo-mechanisms and incorporated in the pulsing system at the. point Where the digital commands are converted into analog commands.

Various other objects, advantages and meritorious features of the invention will become more fully apparent from the following specification, appended claims and accompanying drawings wherein:

FIG. 1 is a general perspective view of a machine tool in the form of a bridge type planer mill and a director unit for controlling the operation of the machine tool.

FIG. 2 is a functional block diagram perspective of the machine tool and its director unit and partially broken away to show the major components thereof and the interconnection therebetween,

FIG. 3 is a simplified block diagram of the overall system of the invention for controlling theoperating parts of a machine tool,

FIG. 4 is a partial block diagram of the control system of the present invention,

FIG. 5 is the balance of the block diagram illustrated in FIG. 4,

FIG. 6 is a simplified block diagram of the clock system schematically illustrating the division of a cycle of pulses generated by a clock oscillator and the modulation thereof by manual or automatic control means,

FIG. 7 is a schematic View in perspective illustrating the automatic data supply system including the manner of reading coded information on punched tape and the distribution of such information to separate banks of storage control registers,

FIG. 8 is a chart illustrating the pulse sequence provided by the initial frequency divider in the clock system,

FIG. 9 is a chart illustrating the pulse sequence provided by the second frequency divider in the clock system,

FIG. 10 is a schematic perspective view illustrating a typical power servo-mechanism for controlling the movement of one of the operating parts of a machine tool,

FIG. 10A illustrates a preferred circuit for the synchro devices,

FIG. 11 is a schematic perspective view of one of the pulse-code-to-analog servo-mechanisms in the control system,

FIG. 12 is a diagrammatic representation of the position coder illustrating how pulses received by the coder are modified to determine the direction of each movement of the machine tool part controlled thereby,

FIG. 13 is a simplified equivalent circuit of the decoder,

FIG. 14 isa block diagram of the divider checking circuit,

FIG. 15 is a block diagram of the summing register,

FIG. 16 is a block diagram of the position-code converter,

FIG. 17 is a plan view of a section of punched tape illustrating the arrangement of holes in two adjacent information blocks,

FIG. 18 is a diagrammatic View of an airfoil panel,

FIG. 19 is a perspective sectional view of the airfoil panel of FIG. 18, illustrating the relation of the cutters center to the workpiece and the three axis coordinates, and

FIG. 20 is a perspective diagram illustrating the correction to be applied to the coordinates to account for noncoincidence of cutter center to point of contact with the workpiece.

Although the control system of th present invention is applicable to other uses, it is herein described as applied to and combined with an industrial machine and specifically a machine tool. A machine tool numerically controlled by the system is designed to serve function which is not available in existing types of such machines. it differs from standard machine tools in that directions of cuts are not limited in lines parallel to the machine-feed directions, but as a result of a positive coordination among the several feed mechanisms it is possible to out along a line inclined or skewed with respect to the feed directions built into the machine. Moreover, such a machine tool differs from contour directed machine tools in that no models or templates are required to perform the coordinated motions in the several directions in which the machine is capable of operating.

The control instructions fed to the machine by the control system may be set in either manually or automatically by means of a control unit referred to as the director. The automatic instructions may be set into the machine on an information storing medium such as punched paper tape, magnetic tape, punched cards, photographic film, et cetera. These instructions are specifications of straightline segments. By suitable coding of the data storing medium, such as punched tape, any curved line within the capabilities of the machine tool can be machined or cut by approximating the curved line by a series of straight-line segments. In addition, instructions to the machine be set in manually at the director. This may be accomplished by means of a plurality of banks of switches which through circuits inform the machine how far it must travel in each coordinate direction and the machine acts upon these instructions to produce a straight-line motion for the specified interval.

FIG. 1 shows a conceptual arrangement of a machine tool and its director. The machine tool illustrated in PEG. 1 and subsequently discussed hereinafter is an example of how this invention may be applied. It is not limited to machines of this character. The illustrated machine tool is a bridge type of planer mill and is generally indicated at 1 9. The director for the machine tool is generally indicated 12 and may be located near the machine tool or remote therefrom.

The particular machine tool illustrated herein has three operating axes functioning in planes perpendicular to one another in order to provide relative movement between the work and the shaping or cutting tool. These axes are referred to respectively as the X, Y and Z axes. The axis in the illustrated embodiment of the invention is utilized to drive a table 14 upon which the work is placed and to move the table relatively horizontally to and fro on a bed 16 having a pair of parallel ways or guide channels i818 of conventional design for this purpose. The Y axis is utilized to drive a part of the machine referred to as the rail Zn in a vertical path above the table 14. The rail is mounted for vertical travel on an inverte generally U-shaped column 22 which is a customary feature of the bridge type or" planer mill. Carried on the rail 20 is a head 24 from which depends a shaping tool which may be a cutter 26. The third axis Z is utilized to drive the head in a to and fro direction along the rail 2% cross-wise to the table 14.

Separate-drive equipment is provided for moving the table 14, rail 20, and the head 24 as shown in FIG. 2, these drive mechanisms may be housed in separate units indicated respectively at 28, 30 and 32. However, as illustrated in FIG. 1, the drive equipment for the table and the rail may be housed in a single unit indicated at 34 at one side of the column 22. Each drive equipment for the separate axes of the machine tool is preferably a power operated servo-mechanism of the character hereinafter described.

The various component parts of the director 12 may be incorporated into a single unit as shown in FIGS. 1 and 2 and located either adjacent to the machine or remote therefrom. The director is electrically connected to the servo drive mechanisms of the machine tool by electric conduits as illustrated in FIG. 2. Separate electrical control channels lead from the director to each of these drive mechanisms, the one for the table drive equipment being indicated at 36; the one for the rail equipment being indicated at 38, and the one for the head drive equipment being indicated at 40. It is understood that the director 12 may be provided with simlar sets of control channels 36, 38 and 40 for controlling one or more additional machine tools.

The director 12 of the control system is sub-divided into a plurality of components which are electrically coupled together for decoding and furnishing command information to the power servo-mechanisms housed in the units 28, 30 and 32, for comparing the resulting operation of the moving part of the machine against the command information furnished thereto, and for checking the components and for indicating any malfunction in the control system. Referring to FIG. 2, the director 12 is broken away to show schematically such components as a clock system 42, an automatic data supply system 44 including a reader 46 for sensing stored information such as on punched tape, a manual data supply system 48, and as many pulse converting servo-mechanisms as there are machine drive axes on the machine such as the three units 50, 52 and 54, referred to as pulse-code-to-analog servo-mechanisms, which separately control the machine drive servomotor units 28, 3t) and 32 respectively as illustrated by the communicating channels 36, 38 and 40 between the director and the milling machine.

The director unit 12 is provided with a front panel as shown in FIG. 1 upon which various control and indicating elements are preferably visibly mounted for actuation and observation 'by the operator. Such control and indicating elements are schematically shown in FIG. 1. The front panel of the director may be sub-divided into panel sections fronting the different components of the director therewithin. For example, one panel section 56 may contain a start and stop control member 58 and associated alarm controls mounted adjacent thereto. Another panel section, such as that indicated at 60, may contain means for manually feeding data into the system including a plurality of toggle switches 62 disposed on the panel section in accessible position. The means for automatically supplying data into the control system, such as the tape reader 46, may be mounted in the director with the front panel section removed in order to render it accessible to use. A front panel section 64 may be provided with a control member 66 for varying the frequency of a pulse generating clock oscillator. Other front panel sections of the director may be provided with power supply controls such as indica-ted at 68 and 70, and with indicating elements 72 associated with summing registers and decoders. All the component parts of the director may be housed in one or more units adjacent to the machine controlled thereby, or they may be separately located from one another and the machine.

FIG. 3 is a simplified block diagram of the control system for a machine tool showing the connections of the major functional elements thereof. For purpose of clarity, a brief reference to the simplified block diagram will show a panel 74 referred to as the central control which functions to start and stop the machine, check signals supplied by the directing elements of the system and as later pointed out hereinafter for indicating any malfunctioning of the machine to the operator. The central control is electrically connected to the clock system 42 previously mentioned which serves as the primary pulse source for the operation of the machine. Included in the clock system as hereinafter described is means for dividing the pulses emitted by the clock system. One set of divided pulses from the clock system is furnished by channel 78 to both the automatic data supply system 44 with which the tape reader 46 or other form of sensing mechanism for reading stored information is associated and to the manual data supply system 48 which, as shown in the block diagram of FIG. 3, is disposed in relatively parallel relationship to the automatic data supply system. Another divided set of pulses from the clock system 42 is conveyed by channel 80 for synchronizing the operation of the pulsecode-to-analog servo-mechanisms in the manner hereinafter described.

The function of the data supply systems 44 and 48 is to convert the instructions either manually applied or automatically furnished on coded tape into controlling signals capable of adjusting or modulating the pulses generated by the clock system in accordance with the instructions received. The resulting adjusted pulses are used as command pulses for controlling the moving parts of the machine with which the director is associated, such as the pulse-code-to-analog servo-mechanisms 5t 52 and 54 of the machine illustrated herein. These servo-mechanisms in turn furnish synchro data to the machine drive servomotors 28, 30 and 32 which as previously described control the moving parts 14, 2d and 24 of the machine tool. Return circuit channels may be provided as indicated in dotted lines at 82, 84 and 86 for the purpose of signalling the data supply system 44 to stop the flow of command pulses in the event of any malfunction preventing proper responses. The checking signals furnished by the channels 82, 84 and are conveyed to the central control 74 as indicated by the ex tensions of the dotted lines to that element. In addition, a return line 88 may be provided which connects the Y axis machine driven servo-mechanism 3% with the central control 74 to furnish a command signal for retracting the cutter under circumstances preventing the stopping of the machine under control.

As herein illustrated, the three power servomotors 28, 30 and 32 perform the function of positioning the shaping tool or cutter 26 with respect to the workpiece on the machine table 14. In terms of the bridge-type of planer mill being considered herein, it is understood from the previous description that one servomotor, such as the unit 28, positions the table in the longitudinal direction; that a second servomotor, such as the unit 3%, positions the rail 243 in a vertical direction with respect to the table; and the third servomotor, such as the unit 32, positions the shaping or cutting tool 26 in the transverse (cross feed) direction of the machine. It is understood that the power units or machine drive servomotors are capable of accomplishing their positioning functions in the presence of cutting force reactions of considerable magnitude.

Group Relation of Functional Components of Control System The general assemblage of the major components of the control system has been heretofore described in connection with FIGS. 1, 2 and 3. There follows a more completely integrated charted representation of the control system and showing its application to one of the pulse-code-to-analog servo-mechanisms and the machine drive servomotor associated therewith. FIGS. 4 and 5 together illustrate a more comprehensive block diagram of the control system showing the functional components of the system and the interconnections therebetween in- 7 eluding control and checking channels as well as the main signal channels.

Referring particul rly to FIGS. 4 and 5, it is noted that PEG. is a continuation of the block diagram of FIG. 4 and shows the interconnection of one pulse-codeto-analog servo-mechanism and the power servomechanisrn controlled thereby with the command, checking and control circuits of l. The pulse-code-to-analog servo-mechanism selected for illustrative purposes is the one controlling motions along the X coordinate of the machine, namely, servomechanism t ll. The machine drive servomechanism 28 is operatively associated therewith and as previously described controls the movement of the machine table It is understood, as shown by the separate command pulse channels leading from the data supply system 24 in PEG. 3 that the two remaining servomechanisms 52 and 5d and their respective servonn era are similarly operatively connected to the command, checking and control circuits of FIG. 4.

The component systems of the director hereinabove described in connection with FIG. 3 are shown in more detail in FIGS. 4 and 5. The box outlines for the components in FIG. 3 are employed in 4 5 but in larger scale and with more particularity. The central control panel 7-4, the clock system 4 2, the automatic data supply system and the manual data supply system 53 are represented. by separate boxes in the block diagram of HS. 4. Similarly, the pulse-code-to-analog servo-mechanism 5d and its associated power servornotor 28 are shown in box outline in FIG. 5.

The several systems illustrated in PEG. 4 are interconnected by comrnand, checking and control circuits as indicated by the various channels running from one to the other. The central control panel 74 contains control elements such as push buttons and indicating elements such as electric lamps which are connected by various c. other; to di 'lerent units of the several systems. Cetain of the control elements serve to start stop the machine and to select either the manual or automatic data supply systems for operation. Electric signal lamps are also provided for identifying any malfunctioning of the machine to the ope .tor.

The clock system 2 includes a clock oscillator 90 which serves as the primary pulse source for the operation of the cont'ol systcn. system are tw $2 and 3.

divider 'viders or pulse distributors, d to as the first frequency equency divider it will i that the clock system has other operating e everal of which are interposed between the two frequency dividers. These operating elerncnts comprise a start-stop circuit 96, a clock cycle control 98, and a divider cneck circuit see. The main channel is directed from the clock oscillator through the initial or first frequency divider 92 thence through the start-stop circuit )6 and the clock cycle control 98 to the second frequency divider 9d. The design and function of the newly cited operating elements of the clock system are described in detail hereinafter.

The clock as 99 generates series of pulses which usually yered regularly spaced in time. Tl ese pulses are sent out to the first frequency divider and thereafter some of the e pulses are delivered to the second freque cy divider Each pulse genera ed. by the clock oscill or potentially represents an instruction to move a part of the machine one unit or" distance. in the ill ated embodiment of the invention not every pulse is us-..d instruction r moving a. controlled element. Usually only a rela ...ly small number of pulses gener ted within a prescribed time are utilized as command pu es as hereinafter" described. Since each pulse chsractcriz a In. veiuent of one unit of dist nce, the oscillator fre ency of the pulses be viewed as a distance per unit of time or a velocity. The pulse requency generated by the clock oscillator may be Also included in the clock i 8 set to correspond to a velocity preferably slightly in excess of the maximum feed rate of the machine under control as hereinafter explained.

The clock oscillator 9d is regulated by the control element 66 on the central control panel 7-4. The purpose of this control element is to obtain variable feed rates for the movable parts of the machine tool. For this purpose, the clock oscillator may be made continuously variable over two bands. One hand of adjustment covers five hundred to twenty-five hundred pulses per second and the other band covers one thousand to five thousand pulses per second. Each pulse generated by the clock oscillator 96 may be of any form but preferably is half sinusoidal and the duration may be ten micro-seconds at its base. The pulses generated by the clock oscillator are conveyed by channel 104 to the first frequency divider In general, the function of the first frequency divider 92 in the clock system is to divide the pulses received from the clock oscillator, sending certain synchronizing pulses out on the channel St) to the pulse-code-to-analog servo-mechanisms and on a channel 442 to the divider check circuit Mill, and the remaining pulses to frequency divider 94. Pulses conveyed to frequency divider 94 are potential command pulses for governing the action of the pulse-code-to-analog servo-mechanisms.

The potential command pulses furnished by the first frequency divider 92 are delivered along the channel 168 in the clocl: system to the unit referred to as the startstop circuit 96. In general, the function of the start-stop circuit is to control the how of potential command pulses to the clock cycle control unit When the machine is ready to operate, a signal conveyed over channel 119 from the control panel 74 to the start-stop circuit allows the flow of pulses on channel 1% to go to the clock cycle control along channel 112. When the machine is to be stopped, a signal from the control panel 74 to the startstop circuit will shut off the flow of pulses from channel The; to channel 112.

in general, the function of the clock cycle control unit 93 in the clock system is to adjust the duration of one clock cycle to the length of the cut desired in one machine cycle. The machine is preferably provided with a choice of a plurality of fixed clock cycles anywhere between 21 maximum duration at the nominal clock cycle rate and a minimum duration of considerable shorter time. In the illustrated embodiment of the invention, the machine has a choice of eight fixed clock cycles be- Ween 2 seconds and 256 seconds in duration. The purpose of providing a plurality of fixed clock cycles is in order to be able to adjust the cycle time long enough to do a particular operation and thus conserve e. For example, the clock cycle control unit may provide a relatively long cycle time for making one long straight line cut from a single block of data on the tape. For making shorter cuts, the clock cycle unit may provide a short cycle time so that the machine does not consume the maximum clock time allotted, such as 256 seconds.

The second frequency divider 94 in the clock system receives its pulses from the clock cycle control over channel 114, and functions to generate on separate lines, a pattern of pulses-which, in accordance with settings in the automatic or manual data supply system, may or may not be used as command pulses for the pulsc-code-to-analog servo-mechanisms. This is explained in detail hereinafter. Those pulses which are used for command pillposes are transmitted over channel 78 to the automatic and manual data supply systems. Frequency divider 94 also generates an end carry pulse which signifies the end of a clock cycle. This last pulse is returned by the channel 116 to the clock cycle control 98 and thence from there along channel 11% to the automatic data supply system 4-4 where as hereinafter described it will signal the tape reader or other data sensing means to advance and read the next successive instruction on the tape.

In general, the divider checking circuit 100 in the clock system functions to check the second frequency divider 94 and the second stage of the first frequency divider 92. It serves to guard against the loss of a possible cornmand pulse and, hence, against integration errors in converting rate commands to position commands. If in checking these frequency dividers, the checking circuit 100 determines there is an unaccounted or missing pulse, it will send out an alarm pulse over channel 120 to the start-stop circuit causing the latter to stop the flow of potential command pulses over channel 112. The two frequency dividers 92 and 94 may be considered together to form a single binary frequency divider of various stages, depending upon the setting of the clock cycle control.

The automatic data supply system 44 as diagrammatically shown in FIG. 4 comprises the tape reader 46, a data distributor 122, a command data converter unit 124 containing banks of information storage registers as hereinafter described, and a manual-automatic control unit 126 from which command pulses are delivered by channel 128. Since in the block diagrams of FIGS. 4 and 5 the control system is shown as governing the action of the pulse-code-to-analog servo-mechanism 50 for the X or table axis and its associated power servomotor 28, FIG. 5 illustrates these two component parts of the system and the delivery of command pulses thereto by way of channel 128. It is understood that the two remaining pulse-code-to-analog servo-mechanisms 52 and 54 and their respective servomotors 30 and 32 are similarly controlled from the data supply systems.

The function of the tape reader 46 or other device for sensing coded information is to convert information stored on tape to a form acceptable to the data distributor 122 and the data converter 124 for each axis of the machine. The reader scans the machine orders on the information storage medium, such as the punched holes in the tape, and converts the pattern of coded information into pulses transmitted simultaneously over a selected combination of output lines over channel 130 and leading from the tape reader to the data distributor 122.

The primary function of the data distributor 122 in the automatic data supply system is to route or distribute the tape reader signals representing successive lines of tape data over channel 132 to the command data converter until 124, *where the corresponding digits of the machine control orders are stored. 'Its secondary functions are to control the tape reader so that the proper number of lines are read from the tape at the proper times, and to signal the control circuits of the panel 74 in the event of certain errors arising in the automatic data supply system.

The function of the command data converter unit 124 is to control the transmission of the proper number of control-register pulses to the separate pulse-code-to-analog servo-mechanisms 50, 52 and 54. In the charted representation illustrated in FIGS. 4 and 5, the control system is shown as applied to the servo-mechanism 50 for actutaing the table 14 of the machine tool along the X axis. The command data converter unit contains two sets or banks of alternately operable registers for each coordinate axis of the controlled machine. The pulses desired from either bank of registers, whichever is in operation during a particular clock cycle, are transmitted over channel 134 to a manual-automatic control unit 126.

The function of the manual-automatic control unit 126 is to determine the source of command pulses for the selected pulse-code-to-analog servo-mechanism. The control unit 126 is actuated to feed pulses from either the automatic or manual data supply systems 44 and 48 by means of a signal sent over channel 136 from the central control panel 74. The manual-automatic control unit 126 may include three relays, one for each axis. These relays may be arranged so that when de-energized the pulses from the manual data supply system are furnished to the selected servo-mechanism and when energized by a signal on channel 136 the relays connect channel 134 to one or more pulse converting servo-mechanisms 50, 52 and 54.

The manual supply data system 48 includes a command data converter unit 138 which functions similarly to the data converter unit 124 to gate the desired pulse rates from channel 78 over which the pulses from frequency divider 94 are transmitted. The manual command data converter may comprise the bank of switches 62 previously described in connection with FIG. 1. In the illustrated embodiment of the invention, eighteen manually operated toggle switches are employed in the bank which will accommodate command orders having seventeen binary digits and the directional sense digit of either a plus or a minus sign. As in the case of automatic data command converter unit 124, the three command numbers for the separate axes of the machine represent the position increment in each axis necessary to move the machine from its present position to a new position.

Each pulse-code-to-analog servo-mechanism of the illustrated embodiment of the invention comprises as shown in the block diagram of FIG. 5 an electrically and mechanically connected group of units referred to as a summing register 140, a decoder 142, an amplifier servomotor 144, a synchro-transmitter 146, and interconnecting servo gearing 148 between the servomotor and the synchro-transmitter. In addition, each pulse-code-toanalog servo-mechanism includes a feed-back mechanism schematically shown in FIG. 5 as a position coder 150 and a position code converter 152. Although the servomotor of the unit 144 may be directly connected to the element or machine part under control, in the illustrated embodiment of the invention each pulse-code-to-analog servo-mechanism operates through a machine drive servomechanism, such as shown in block outline in the lower portion of FIG. 5.

Each machine drive servo-mechanism is shown in the present form of the invention as comprising a synchro receiver 154, an amplifier and servomotor 156, and machine feed gearing 158 connecting the servomotor with the controlled part of the machine. In addition, each machine drive servo-mechanism includes machine data gearing generally indicated at 160 and limit stops characterized by the box outline at 162. Synchronizing data is transmitted between the pulse-code-to-analog servomechanism and its associated machine drive servo-mechanism over channel 164.

It is to be noted that command pulses delivered over channel 128 from the automatic data supply system 44 are directed to the summing register 140 where they are compared against response pulses arising out of the position code converter 152. The channel over which synchronizing pulses are sent from the first frequency divider 92 is connected to both the position code converter 152 and the position coder 150.

Clock System and Control Registers FIG. 6 illustrates a simplified schematic block diagram of the operating relation between the clock system and the control registers of the data supply system and is intended to illustrate how the instructions, whether recorded on storage medium, such as punched tape and the like, or manually operated, are converted into a series of pulses which serve as the input to controlled elements such as the servo-mechanisms 50, '52 and 54. The basic parts of this operating relationship are embodied in four principal units: the master or clock oscillator forming part of the clock system 4 2 described in connection with FIG. 4; the pulse distributor generally referred to as the first frequency divider )2; the pulse distributor generally referred to as the second frequency divider 94; a pulse 

